The present invention relates generally to an apparatus and method for inserting and retrieving pipeline pigs into pipelines, and more specifically to an apparatus and method for installing an in-line piggable wye fitting into a pipeline for the insertion and removal of in-line inspections tools.
The primary purpose of pipeline pigs is to clean and obtain vital information concerning the integrity of the pipeline. The pigs used in most oil and liquid products pipelines are typically used to remove paraffins, sludge, and water from the pipeline. The most common pigs that are used in oil and liquid products pipelines are in the shape of spheres or bullets that are made of a polyurethane material. As a result, these foam pigs are lightweight, easy to work with, and able to negotiate uncommon piping, fittings, and valves. Other types of cleaning pigs are solid cast pigs and steel mandrel scraper pigs. In other applications, such as oil and gas and natural gas pipelines, intelligent pigs (also called in-line inspection (ILI) tools) are used to determine the integrity of the pipe wall for such conditions as corrosion, wall thinning, and other defects that may affect the pipeline operations. Common types of these intelligent pigs include ultrasonic (UT) and magnetic flux leakage (MFL) induced sensors, such as the SmartScan sensors made by GE and many others well known in the art.
A pig must be launched into the pipeline for cleaning or inspection (typically by a launching station) and removed from the pipeline (typically by a receiving station) to allow for normal operation of the pipeline when the pig is in the pipeline. The pig is typically introduced into the pipeline by means of a bypass loop that diverts the flow of the pipeline product to the launch vessel by the use of valves and other pipeworks. When the pipeline product is diverted to the launcher, a valve downstream of the launcher is opened and the pig is introduced into the pipeline by means of the launching station. In most cases, the tool travels along the length of the pipeline with special seals that allow the product flowing in the pipeline to push the tool. As the tool travels, it cleans the pipeline and/or performs inspections on the pipeline and is received into the receiving vessel at the end of the pipeline run. The receiver is similar to the launcher in that a bypass loop is established with valving and pipeworks to divert the tool into the receiver without substantially disrupting the pipeline operations. In most oil and liquid products pipelines, launch and receive stations are permanently installed at various locations during installation of the pipelines to allow the cleaning of paraffin deposits and other mineral build-ups. Because the valving and pipeworks of these pipeline systems were designed for the use of pigs (i.e., the valves in these pipelines typically include an orifice the same size as the internal pipeline and consistently sized piping was used between launch and receive stations), the pigs are able to inspect a long length of pipeline between the launch and receive stations.
The most comprehensive method to give an overall assessment of a natural gas and crude pipeline is to run intelligent pigs that can map many inspection points along the internal length of the pipeline. The challenge in using intelligent pigs in these pipelines is the piping configurations that prevented previous technologies from gathering the required information on a cost effective basis, often called “unpiggable” pipelines. Pipelines can be “unpiggable” for a variety of reasons, including changes in diameter (because of compressibility of gas, the use of multi-diameter pipes is common), presence of unsuitable valves, tight or mitered bends (less than three diameters), low operating pressure, low flow or absence of flow, lack of launching and receiving facilities, dented or collapsed areas, and excessive debris or scale build-up. Natural gas pipelines are particularly known for having a high number of “unpiggable” pipelines. Further, in natural gas pipelines, products rarely produced deposits onto the pipe walls and did not require cleaning during the service life of the pipelines. Thus, the use of pipeline cleaning or in-line inspection pigs, and the use and installation of launch and receive stations, were traditionally not common in natural gas pipelines. Rather, the integrity of the pipeline was monitored by various means such as by using sacrificial corrosion coupons (e.g., pipe samples taken from the pipeline wall), visual inspection, and/or digs to perform pipe wall thickness analyses to predict corrosion rates. Unfortunately, these methods are only indicative of the conditions at the specific spots of inspection.
Techniques were developed for a method and system that uses “hot tap” technology to access the existing pipeline by adding a new connection to the pipeline without interruption of service. In this technique, after a 45 degree hot tap is made in the pipeline, a chute housing is connected to the hot tap valve. The chute within the housing is inserted through the hot tap valve to provide a path for the inspection tool to follow into the pipeline. After the chute is inserted, the bypass piping with the launch vessel is assembled to the pipeline and chute housing, and gas is allowed to flow from the pipeline so as to enter behind the inspection tool. The mainline valve is closed and the bypass valve is opened launching the tool into the pipeline. The inspection tool proceeds through the pipeline performing pipeline integrity tests and then is removed from the pipeline when it enters into the receiver station that is substantially similar to the launch station. At both the launching and receiving sites, the chute is retracted and the chute housing and associated pipeworks are removed prior to insertion of the completion plugs. The completion plugs are set to allow the hot tap valves to be removed. Once the completion plug is set, a blind flange is installed and the pipeline can be covered. A similar system is described in WO 2005/119117, incorporated herein by reference.
Although this “hot tap” method has been used in industry, it suffers from numerous and significant disadvantages. The complexity of the hot tap technique for insertion of launch and receive vessels to be connected to chute housings requires customization for every application. Another primary disadvantage is that the equipment for introducing and retrieving an inspection tool into and from a pipeline by the hot tap method are extremely large and heavy. The chute housings with the actuators can extend over 50 feet above the pipeline requiring considerable lifting capabilities as well as supports for the equipment. Using this equipment requires detailed planning for transportation, assembly, and use, such as acquiring right of ways for transportation of the equipment to the work site. Additionally, the equipment is limited in application due to the complexity of the tool geometry, which lends itself to larger diameter pipelines, so inspection tools typically cannot not be inserted into smaller diameter pipelines according to this “hot tap” method. Another problem is the high cost for the use of such chute housings and launch and receive vessels and associated methods for use and installation. Typical launch/receive stations (including the chute housings) for this “hot tap” method require a large investment in piping and facilities with little payback, and often run into the millions of dollars per station. As a result, many pipelines cannot be efficiently and/or effectively inspected, if even inspected at all.
What is needed is an apparatus and method for inserting a pig or inline inspection tool into a pipeline that will simplify the design, installation, and operation of fittings and associated pipeworks for launching/receiving inspection tools, reduce installation time of such equipment, reduce the equipment size, allow for temporary launch/receive facilities, reduce capital and operating costs, allow for inspection of previously unpiggable pipes (such as smaller diameter pipelines), and allow for more frequent and easier insertion and removal of tools into the pipeline.